The present invention relates to a method of installing optical fibres in duct systems or like tubular systems, and also to a device for installing optical fibres in duct systems or like tubular systems. The invention is conceived for use preferably in installing optical fibres in a duct system provided in connection with living accommodation building structures, such as in apartment blocks or like buildings.
It is known to blow optical fibres through ducts or like tubular runways with the aid of pressurised air, for instance when installing optical fibres in the apartments of an apartment block. The pressurised air is normally delivered to a duct location at which the optical fibre is introduced, and there transforms into an air flow which engages around the fibre and drives the fibre forwards in the duct. The speed at which the optical fibre is fed through the duct can be controlled by correspondingly adapting the air pressure, and therewith the power of the air flow acting on the fibre.
Earlier publications EP 0 319 194 A1 and GB 2 152 621 A teach methods and devices for sucking optical fibres into a duct with the aid of a suction device which generates subpressure in the duct for advancement of the fibre in the duct.
With the intention of simplifying the handling of optical fibres when installing optical fibres in duct systems that lead to outlets in various residential spaces in an apartment block for instance, there has been applied to this end a subpressure generated by a suction device located at a central collecting point which is common to all optical fibres in the duct system, such as a fibre accommodating star duct system, therewith obviating the need to move the suction device between the various optical fibre input points, as distinct from the case when the optical fibres are blown into said ducts, and also obviating the need of separate nozzles for different types of optical fibres, as distinct from the case when blowing optical fibres into the ducts. By first providing each connection point and outlet in respective apartments with a store of optical fibres that have been previously connected electrically at one end, and then drawing one optical fibre or a number of optical fibres simultaneously from the store of optical fibres to said collecting point, the optical fibre or said several optical fibres can be installed in the duct system by means of one single workman. The end of each optical fibre can then be connected at said connecting point to an optical fibre connecting device provided at said point. Suction of optical fibres into duct systems eliminates problems that occur when blowing said fibres into the ducts, such as the ingress of water or oil into the ducts from the blower or the compressor. The use of subpressure also simplifies connection of the ducts to the optical fibres. The ducts can be readily joined, by simply placing a rubber hose joint around the duct joins.
The present invention differs form the earlier known fibre blow-in methods by virtue of the fact that in accordance with the invention the optical fibres are sucked into an installed duct system that includes a centrally arranged suction device, as distinct from known methods in which the optical fibres are blown individually into the various ducts of the duct system.
In principle, suction of the optical fibres into a duct system is based on similar physiological laws that apply when blowing optical fibres into said system, in other words on the basis of a pressure difference that acts between the two end openings of the existing duct that is created by an air flow therein, where said pressure difference strives to achieve equilibrium. Different pressure conditions and different air flows can be obtained, by controlling the suction force through the medium of a suction device connected to the duct. A pulling force can be generated in one end of the optical fibre, with the aid of a body in the form of a plastic pilot device that has a rounded top and mounted on said fibre end. The magnitude of this pulling force will depend partially on the magnitude of the xe2x80x9cpneumatic resistancexe2x80x9d exerted by the body/pilot device. This resistance can be regulated by appropriate dimensioning of the body/pilot device concerned. A combination of an existing pressure difference and a suitable pilot device can provide the most favourable conditions between the pulling force on said end of the optical fibre and the frictional forces that occur between the air passing through the duct and the optical fibre present therein. One important advantage obtained with sucking optical fibres through ducts instead of blowing the fibres therethrough is that no separate nozzles are required for different types of optical fibres. Another advantage is that no xe2x80x9creverse air flowxe2x80x9d occurs, as distinct to the case when blowing optical fibres through the ducts.
Feeding of the optical fibre or the optical fibres through a duct system is achieved with the aid of the pulling forces exerted by the pilot device on said fibre or fibres and/or with the aid of the aerodynamic influence of the air flow on said fibre or fibres. The pulling forces occurring in the optical fibres are generally marginal and will not have any undue effect thereon.
The length of optical fibre required, including any necessary additional length, is coiled onto a static unwinding drum or like device at the end of the duct into which the optical fibre shall be fed. Subsequent to having generated a sufficiently large subpressure in the duct, the end of the optical fibre is inserted into the duct and therewith advance along the duct, said fibre end possibly being provided with a tuft of appropriate material. The fibre infeed sequence can be easily controlled, by lightly retarding the speed at which the optical fibre is fed into the duct. When practically all of the fibre length has been drawn through the duct, insertion of further fibre is stopped, either by braking advancement of the fibre or by switching off the device used to generate the necessary subpressure. The optical fibre or optical fibre ribbon sucked into the duct may be of a single mode or a multimode type and may have been fitted with an electric contact device at one end/the final end. A collecting container for collecting any optical fibre surplus may be placed at the end of the duct at which the suction device is located, said container optionally being connected to said suction device. A filter will preferably be connected between the suction device and the collecting vessel. The collecting vessel will preferably be dimensioned to adequately accommodate an optical fibre surplus and will be constructed so as to enable the interior of the container to be seen. The invention is preferably intended for use in the xe2x80x9cshort distance installationxe2x80x9d of optical fibres. The invention can also be applied in respect of optical fibre cable elements which include several optical fibres that are held together with helically overlapping bands, and also in respect of optical fibre ribbons, such ribbons being much more robust than individual optical fibres and have greater tensile strength.
Suction feeding of optical fibres in duct systems also enables two different optical fibres to be readily joined or connected in two meeting ducts, by connecting the two inner duct-ends to the suction device and introducing the optical fibres into respective outer duct-ends. When the ends of the optical fibres have met between the two inner duct-ends, the fibres can be joined together or connected to a connecting device located at said meeting place.
Typical installation lengths will be less than 50 meters. As a result of the present invention, the optical fibre need not be specially treated prior to installation in order to improve suction properties, and it is possible to use a standard optical fibre. A typical installation case is an apartment in which different outlets having optical termination points in the form of wall sockets shall be installed. Fibre installation can be simplified with the aid of so-called fibre ducts or tubular fibre runways that have been installed in the apartment concerned, either in existing channelling or directly in a space located in a partition wall. The fibre ducts are provided with a number of branch ducts (Y pipes) at the planned wall outlets along the ducts. The inlets to the various Y pipes are plugged temporarily and when a subpressure is applied at the central connecting point in the apartment, one or more optical fibres can be fed into the duct at the distal wall outlet. Upon completion of the first fibre suction operation, the optical fibre/optical fibres is/are fixed in the opening and the opening between duct and optical fibre, optical fibres or optical fibre ribbon is closed. The plug at the next distal wall outlet is then removed and an optical fibre or optical fibres is/are sucked in therefrom, this procedure being repeated until installation is complete. The use of standard optical fibre ribbons having a smooth and slippery acrylate cover for instance will enable an optical fibre ribbon sucked through a duct to pass by an earlier installed optical fibre ribbon in the process. The optical fibres or ribbons may be treated with an antistatic agent, such as a lubricant or talcum powder, to avoid the fibres or ribbons from sticking in the duct as a result of to static electricity. Because only one suction device is used, the suction device can be placed centrally and need not be moved from its initial position, as distinct to when the fibres are blown through respective ducts and where it is necessary to position a compressor at respective blow-in locations.